Etching method and plasma processing apparatus

ABSTRACT

An etching method is performed in a state where a substrate is placed on a substrate support provided in a chamber of a plasma processing apparatus. In the etching method, radio-frequency power is supplied to generate plasma from a gas in the chamber. Subsequently, a negative DC voltage is applied to a lower electrode of the substrate support during the supplying of the radio-frequency power to etch the substrate with positive ions from plasma. Subsequently, the applying of the negative DC voltage to the lower electrode and the supplying of the radio-frequency power are stopped to generate negative ions. Subsequently, a positive DC voltage is applied to the lower electrode in a state where the supply of the radio-frequency power is stopped to supply the negative ions to the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese PatentApplication Nos. 2018-208005 and 2019-185832, filed on Nov. 5, 2018 andOct. 9, 2019, respectively, with the Japan Patent Office, thedisclosures of which are incorporated herein in their entireties byreference.

TECHNICAL FIELD

The present disclosure relates to an etching method and a plasmaprocessing apparatus.

BACKGROUND

A plasma processing apparatus used in a plasma etching of a substrateincludes a chamber and a substrate support. The substrate supportincludes a lower electrode and is provided in the chamber. Plasma isgenerated from the gas in the chamber where the substrate is placed onthe substrate support for etching. The substrate is etched by thepositive ions from the plasma to form openings in the substrate.

The substrate is charged as the etching of the substrate with thepositive ions progressed. In a state where the substrate is charged, theamount of positive ions supplied into the openings decreases. As aresult, the etching rate may be reduced. A shape abnormality may alsooccur in the openings formed in the substrate.

In the technique described in Japanese Patent Laid-Open Publication No.2012-079886, a positive DC voltage is applied from a power source to alower electrode in order to reduce the positive charge amount of asubstrate. Subsequently, the application of the DC voltage to the lowerelectrode is stopped. Subsequently, a negative DC voltage is appliedfrom a power supply to the lower electrode. As a result, positive ionsare drawn into the substrate and etching is performed. Thereafter, theapplication of the DC voltage to the lower electrode is stopped. In thetechnique described in Japanese Patent Laid-Open Publication No.2012-079886, the application of the positive DC voltage to the lowerelectrode, the stop of the application of the DC voltage to the lowerelectrode, the application of the negative DC voltage to the lowerelectrode, and the stop of the application of the DC voltage to thelower electrode are repeated. The radio-frequency power that generatesplasma is continuously supplied when the application of the positive DCvoltage to the lower electrode, the stop of the application of the DCvoltage to the lower electrode, the application of the negative DCvoltage to the lower electrode, and the stop of the application of theDC voltage to the lower electrode are repeated.

SUMMARY

In an embodiment, an etching method performed in a plasma processingapparatus is provided. The etching method is performed in a state inwhich a substrate is placed on a substrate support provided in a chamberof the plasma processing apparatus. The etching method includessupplying radio-frequency power to generate plasma from a gas in thechamber. The etching method further includes applying a negative DCvoltage to a lower electrode of the substrate support during executionof the supply of radio-frequency power in order to etch the substratewith positive ions from plasma. The etching method further includesstopping the application of the negative DC voltage to the lowerelectrode and the supply of the radio-frequency power in order togenerate negative ions. The etching method further includes applying apositive DC voltage to the lower electrode in a state where the supplyof radio-frequency power is stopped in order to supply negative ions tothe substrate.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating an etching method according to anembodiment.

FIG. 2 is a diagram schematically illustrating a plasma processingapparatus according to an embodiment.

FIG. 3 is a timing chart of an example related to the etching methodillustrated in FIG. 1.

FIG. 4A is a diagram illustrating the state of plasma and a substrate ina period P1 in the timing chart of FIG. 3, and FIG. 4B is a diagramillustrating the state plasma and a substrate in a period P2 in thetiming chart of FIG. 3.

FIG. 5A is a diagram illustrating the state of plasma and a substrate ina period P31 in the timing chart of FIG. 3, and FIG. 5B is a diagramillustrating the state plasma and a substrate in a period P32 in thetiming chart of FIG. 3.

FIG. 6A is a diagram illustrating the state of plasma and a substrate ina period P4 in the timing chart of FIG. 3, and FIG. 6B is a diagram forexplaining step ST5 of the etching method illustrated in FIG. 1.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof. The illustrativeexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other exemplary embodiments maybe utilized, and other changes may be made without departing from thespirit or scope of the subject matter presented here.

Various exemplary embodiments will be described below.

In an embodiment, an etching method performed using a plasma processingapparatus is provided. The etching method is performed in a state inwhich a substrate is placed on a substrate support provided in thechamber of the plasma processing apparatus. The etching method includessupplying radio-frequency power to generate plasma from a gas in thechamber. The etching method further includes applying a negative DCvoltage to a lower electrode of the substrate support during theexecution of the supply of radio-frequency power in order to etch thesubstrate with positive ions from plasma. The etching method furtherincludes stopping the application of the negative DC voltage to thelower electrode and the supply of the radio-frequency power in order togenerate negative ions. The etching method further includes applying apositive DC voltage to the lower electrode in a state where the supplyof radio-frequency power is stopped in order to supply negative ions tothe substrate.

In the above embodiment, a negative DC voltage is supplied to the lowerelectrode in a state where plasma is generated by the supply ofradio-frequency power. As a result, positive ions collide with thesubstrate so as to etch the substrate. Subsequently, the supply of theradio-frequency power and the application of the DC voltage to the lowerelectrode are stopped. Although the amount of negative ions generated issmall in a state where radio-frequency power is supplied, negative ionsare efficiently generated by electrons which are attached to chemicalspecies in the gas when the supply of radio-frequency power is stopped.Subsequently, a positive DC voltage is applied to the lower electrode ina state where the supply of radio-frequency power is stopped. As aresult, negative ions are supplied to the substrate. According to theabove embodiment, the negative ions decrease the positive charge amountof the substrate. Also, the substrate is etched using both positive ionsand negative ions. Therefore, the etching efficiency is improved.

In an embodiment, the etching method may further include exhausting agas from the interior space of the chamber. The discharging step isexecuted after one or more executions of an etching sequence includingsupplying radio-frequency power, applying a negative DC voltage,stopping, and applying a positive DC voltage. At the time of executingthe discharging step, the supply of the radio-frequency power is stoppedand the application of the DC voltage to the lower electrode is stopped.

In an embodiment, another sequence may be repeated that includes one ormore executions of the etching sequence and the discharging step.

In an embodiment, the discharging step may be executed for 10 μsec ormore in the execution period of the other sequence. In the embodiment,etching byproducts are more reliably discharged. As a result, theetching efficiency of the substrate is further improved.

In an embodiment, the time length of the execution period of thedischarging step may be increased as the number of executions of theother sequence increases. In the embodiment, as the depth of the openingformed in the substrate increases, the time length of the executionperiod of the discharging step is increased. Therefore, etchingbyproducts are more reliably discharged.

In an embodiment, a parameter representing an electron density in thechamber may be measured during execution of the stopping step. The stepof applying the positive DC voltage may be started when it is determinedfrom the parameter that the electron density in the chamber is decreasedto satisfy a predetermined standard. The decrease in electron densityduring the stopping step reflects an increase in the amount of negativeions. Therefore, according to the embodiment, the step of applying thepositive DC voltage is started when it is determined that the negativeions are sufficiently generated.

In an embodiment, in the stopping step, the application of the negativeDC voltage to the lower electrode may be stopped before the supply ofthe radio-frequency power is stopped. According to the embodiment, anabnormal discharge is more reliably prevented.

In another embodiment, a plasma processing apparatus is provided. Theplasma processing apparatus includes a chamber, a substrate support, aradio-frequency power source, a power supply unit, and a controller. Thesubstrate support has a lower electrode and is provided in the chamber.The radio-frequency power source is configured to supply radio-frequencypower to generate plasma from a gas in the chamber. The power supplyunit is configured to generate a positive DC voltage and a negative DCvoltage. The power supply unit is electrically connected to the lowerelectrode. The controller is configured to control the radio-frequencypower source and the power supply unit. The controller is configured toexecute a first control, a second control, a third control, and a fourthcontrol. The first control includes controlling the radio-frequencypower source to supply radio-frequency power to generate plasma from thegas in the chamber. The second control includes controlling the powersupply unit so as to apply a negative DC voltage to the lower electrodeof the substrate support during the supply of the radio-frequency powerin order to etch the substrate with positive ions from the plasma. Thethird control includes controlling the power supply unit and theradio-frequency power source to stop the application of the negative DCvoltage to the lower electrode and the supply of the radio-frequencypower in order to generate negative ions. The fourth control includescontrolling the power supply unit so as to apply a positive DC voltageto the lower electrode in a state where the supply of radio-frequencypower is stopped in order to supply negative ions to the substrate.

In an embodiment, the plasma processing apparatus may further include anexhaust device connected to the chamber. The controller may beconfigured to further execute a fifth control. The fifth controlincludes controlling the exhaust device to exhaust a gas from theinternal space of the chamber. The fifth control is executed after oneor more executions of the etching control sequence including the firstcontrol, the second control, the third control, and the fourth control.When the fifth control is executed, the supply of radio-frequency poweris stopped, and the application of the DC voltage to the lower electrodeis stopped.

In an embodiment, the controller may repeatedly execute another controlsequence including one or more executions of the etching controlsequence and the fifth control.

In an embodiment, the fifth control may be executed for 10 μsec or morein the execution period of the other control sequence.

In an embodiment, the controller may increase the time length of theexecution period of the fifth control as the number of executions of theother control sequence increases.

In an embodiment, the plasma processing apparatus may further include ameasuring device. The measuring device measures a parameter representingthe electron density in the chamber during execution of the thirdcontrol. The controller may start the execution of the fourth controlwhen it is determined from the parameter that the electron density inthe chamber is decreased to satisfy a predetermined standard.

In an embodiment, in the third control, the controller may control thepower supply unit to stop applying the negative DC voltage to the lowerelectrode before stopping the supply of the radio-frequency power.

Various embodiments will now be described in detail with reference tothe drawings. Further, in the respective drawings, the same orcorresponding parts will be denoted by the same symbols.

FIG. 1 is a flowchart illustrating an etching method according to anembodiment. The etching method illustrated in FIG. 1 (hereinafter,referred to as a “method MT”) is performed using a plasma processingapparatus. FIG. 2 is a diagram schematically illustrating a plasmaprocessing apparatus according to an embodiment. The plasma processingapparatus 1 illustrated in FIG. 2 may be used to execute the method MT.

The plasma processing apparatus 1 is a capacitively coupled plasmaprocessing apparatus. The plasma processing apparatus 1 includes achamber 10. The chamber 10 provides an internal space 10 s therein. Inthe embodiment, the chamber 10 includes a chamber body 12. The chamberbody 12 has a substantially cylindrical shape. The internal space 10 sis provided in the chamber body 12. The chamber body 12 is made of, forexample, aluminum. The chamber body 12 is electrically grounded. Aplasma-resistant film is formed on the inner wall surface of the chamberbody 12, that is, the wall surface that defines the internal space 10 s.The film may be a ceramic film such as a film formed by anodization or afilm formed from yttrium oxide.

A passage 12 p is formed in the side wall of the chamber body 12. Asubstrate W passes through the passage 12 p when being transferredbetween the internal space 10 s and the outside of the chamber 10. Agate valve 12 g is provided along the side wall of the chamber body 12so as to open and close the passage 12 p.

A substrate support, that is, a support stage 16 is provided in thechamber 10. The support stage 16 is configured to support the substrateW placed thereon. The substrate W has a substantially disk shape. Thesupport stage 16 is supported by a support body 15. The support body 15extends upward from the bottom of the chamber body 12. The chamber body15 has a substantially cylindrical shape. The support body 15 is made ofan insulating material such as quartz.

The support stage 16 has a lower electrode 18. The support stage 16 mayfurther include an electrostatic chuck 20. The support stage 16 mayfurther include an electrode plate 19. The electrode plate 19 is made ofa conductive material such as aluminum and has a substantially diskshape. The lower electrode 18 is provided on the electrode plate 19. Thelower electrode 18 is made of a conductive material such as aluminum andhas a substantially disk shape. The lower electrode 18 is electricallyconnected to the electrode plate 19.

A flow path 18 f is formed in the lower electrode 18. The flow path 18 fis a flow path for the heat exchange medium. As for the heat exchangemedium, a liquid refrigerant or a refrigerant that cools the lowerelectrode 18 by vaporization thereof (e.g., chlorofluorocarbon) is used.A circulation device of the heat exchange medium (e.g., a chiller unit)is connected to the flow path 18 f. The circulation device is providedoutside the chamber 10. A heat exchange medium is supplied to the flowpath 18 f from the circulation device through a pipe 23 a. The heatexchange medium supplied to the flow path 18 f is returned to thecirculation device through a pipe 23 b.

The electrostatic chuck 20 is provided on the lower electrode 18. Whenthe substrate W is processed in the internal space 10 s, the substrate Wis placed on the electrostatic chuck 20 and held by the electrostaticchuck 20. The electrostatic chuck 20 has a main body and electrodes. Themain body of the electrostatic chuck 20 is made of a dielectric such asaluminum oxide or aluminum nitride. The main body of the electrostaticchuck 20 has a substantially disk shape. The electrostatic chuck 20includes a substrate placement region and a focus ring mounting region.The substrate placement region is a region having a substantially diskshape. The upper surface of the substrate placement region extends alonga horizontal plane. An axis AX that includes the center of the substrateplacement region and extends in the vertical direction substantiallycoincides with the center axis of the chamber 10. The substrate W isplaced on the upper surface of the substrate placement region whenprocessed in the chamber 10.

The focus ring mounting region extends in the circumferential directionto surround the substrate mounting region. A focus ring FR is mounted onthe upper surface of the focus ring mounting region. The focus ring FRhas a ring shape. The substrate W is disposed in a region surrounded bythe focus ring FR. That is, the focus ring FR surrounds the edge of thesubstrate W placed on the substrate placement region of theelectrostatic chuck 20. The focus ring FR is made of, for example,silicon or silicon carbide.

The electrode of the electrostatic chuck 20 is provided in the main bodyof the electrostatic chuck 20. The electrode of the electrostatic chuck20 is a film formed from a conductor. A DC power supply is electricallyconnected to the electrode of the electrostatic chuck 20. When a DCvoltage is applied from a DC power source to the electrode of theelectrostatic chuck 20, an electrostatic attraction is generated betweenthe electrostatic chuck 20 and the substrate W. Due to the generatedelectrostatic attraction, the substrate W is attracted to theelectrostatic chuck 20 and held by the electrostatic chuck 20.

The plasma processing apparatus 1 may further include a gas supply line25. The gas supply line 25 supplies a heat transfer gas from a gassupply mechanism, for example, He gas, between the upper surface of theelectrostatic chuck 20 and the back surface (lower surface) of thesubstrate W.

The plasma processing apparatus 1 may further include a tubular portion28 and an insulating portion 29. The tubular portion 28 extends upwardfrom the bottom of the chamber body 12. The tubular portion 28 extendsalong the outer periphery of the support body 15. The tubular portion 28is made of a conductive material and has a substantially cylindricalshape. The tubular portion 28 is electrically grounded. The insulatingportion 29 is provided on the tubular portion 28. The insulating portion29 is made of an insulating material. The insulating portion 29 is madeof ceramic such as, for example, quartz. The insulating portion 29 has asubstantially cylindrical shape. The insulating portion 29 extends alongthe outer periphery of the electrode plate 19, the outer periphery ofthe lower electrode 18, and the outer periphery of the electrostaticchuck 20.

The plasma processing apparatus 1 further includes an upper electrode30. The upper electrode 30 is provided above the support stage 16. Theupper electrode 30 closes an upper opening of the chamber body 12. Theupper electrode 30 is supported on the upper portion of the chamber body12.

The upper electrode 30 includes a top plate 34 and a support body 36.The lower surface of the top plate 34 defines an internal space 10 s. Aplurality of gas discharge holes 34 a are formed in the top plate 34.Each of the plurality of gas discharge holes 34 a penetrates the topplate 34 in the plate thickness direction (vertical direction). Althoughthe top plate 34 is not limited, the top plate 34 is formed from, forexample, silicon. Alternatively, the top plate 34 may have a structurein which a plasma-resistant film is provided on the surface of analuminum member. The film may be a ceramic film such as a film formed byanodization or a film formed from yttrium oxide.

The support body 36 detachably supports the top plate 34. The supportbody 36 is made of a conductive material such as, for example, aluminum.A gas diffusion chamber 36 a is provided inside the support body 36. Aplurality of gas holes 36 b extend downward from the gas diffusionchamber 36 a. The plurality of gas holes 36 b communicate with theplurality of gas discharge holes 34 a, respectively. A gas introductionport 36 c is formed in the support body 36. The gas introduction port 36c is connected to the gas diffusion chamber 36 a. A gas supply pipe 38is connected to the gas introduction port 36 c.

A gas source group 40 is connected to the gas supply pipe 38 via a valvegroup 41, a flow rate controller group 42, and a valve group 43. The gassource group 40, the valve group 41, the flow rate controller group 42,and the valve group 43 constitute a gas supply. The gas source group 40includes a plurality of gas sources. The plurality of gas sourcesinclude one or more gas sources used in etching methods according tovarious embodiments. Each of the valve group 41 and the valve group 43includes a plurality of valves (e.g., open/close valves). The flow ratecontroller group 42 includes a plurality of flow rate controllers. Eachof the plurality of flow controllers in the flow controller group 42 isa mass flow controller or a pressure control type flow controller. Eachof the plurality of gas sources of the gas source group 40 is connectedto the gas supply pipe 38 via a corresponding valve of the valve group41, a corresponding flow rate controller of the flow rate controllergroup 42, and a corresponding valve of the valve group 43. The plasmaprocessing apparatus 1 may supply the gas from one or more gas sourcesselected from the plurality of gas sources of the gas source group 40 tothe internal space 10 s at individually adjusted flow rates.

A baffle member 48 is provided between the tubular portion 28 and theside wall of the chamber body 12. The baffle member 48 may be aplate-like member. The baffle member 48 may be configured by coating,for example, a plate made of aluminum with a ceramic such as yttriumoxide. The baffle member 48 has a plurality of through holes. Below thebaffle member 48, an exhaust pipe 52 is connected to the bottom of thechamber body 12. An exhaust device 50 is connected to the exhaust pipe52. The exhaust device 50 includes a pressure controller such as anautomatic pressure control valve and a vacuum pump such as a turbomolecular pump, and may reduce the pressure in the internal space 10 s.

The plasma processing apparatus 1 further includes a radio-frequencypower source 61. The radio-frequency power source 61 is a power sourcethat generates radio-frequency power for plasma generation. Thefrequency of the radio-frequency power is not limited, but is afrequency within a range of 27 to 100 MHz, for example, 40 MHz or 60MHz. The radio-frequency power source 61 is connected to the lowerelectrode 18 through a matcher 63 and the electrode plate 19 in order tosupply radio-frequency power to the lower electrode 18. The matcher 63has a matching circuit that matches the output impedance of theradio-frequency power source 61 with the impedance on the load side(lower electrode 18 side). Further, the radio-frequency power source 61may not be electrically connected to the lower electrode 18, and may beconnected to the upper electrode 30 via the matcher 63.

The plasma processing apparatus 1 further includes a power supply unit64. The power supply unit 64 is configured to generate a DC voltageapplied to the lower electrode 18. The power supply unit 64 isconfigured to generate a negative DC voltage and a positive DC voltage.The power supply unit 64 is electrically connected to the lowerelectrode 18. In an embodiment, the power supply unit 64 is connected toan electrical path that connects the matcher 63 and the electrode plate19 to each other via a low-path filter 66.

In the plasma processing apparatus 1, a gas is supplied to the internalspace 10 s. In addition, radio-frequency power is supplied to excite gasin the internal space 10 s. As a result, plasma is generated in theinternal space 10 s. The substrate W is processed by chemical speciessuch as ions and/or radicals from the generated plasma.

In an embodiment, the plasma processing apparatus 1 may further includea measuring device 70. The measuring device 70 is configured to measurea parameter representing the electron density in the chamber 10. In anexample, the measuring device 70 is a plasma absorption probe. In theexample, the measuring device 70 includes a network analyzer 70 a, ahigh-pass filter 70 f, and a probe 70 p. The probe 70 p extends from theoutside of the chamber 10 to the inside of the chamber 10. The networkanalyzer 70 a is connected to the probe 70 p through the high-passfilter 70 f. The network analyzer 70 a supplies a weak powerelectromagnetic wave signal to the probe 70 p while changing itsfrequency, and acquires an S11 parameter from the reflected signalreturned from the probe 70 p. The network analyzer 70 a specifies theelectron density in the chamber 10 from the frequency corresponding tothe minimum peak of the S11 parameter in the frequency characteristic ofthe S11 parameter. The specified electron density is used by acontroller MC (to be described later) as a parameter representing theelectron density.

The measuring device 70 is not limited to a plasma absorption probe. Inanother example, the measuring device 70 may be an emissionspectroscopic analyzer. In the example, the measuring device 70specifies the electron density in the chamber 10 from the plasmaemission intensity. In yet another example, the measuring device 70 maybe a device that specifies the electron density in the chamber 10 usinglaser light.

The plasma processing apparatus 1 further includes a controller MC. Thecontroller MC is a computer that includes a processor, a storage device,an input device, a display device, and the like, and controls therespective units of the plasma processing apparatus 1. Specifically, thecontroller MC executes a control program stored in the storage device,and controls the respective units of the plasma processing apparatus 1based on recipe data stored in the storage device. A process designatedby the recipe data is executed in the plasma processing apparatus 1 bythe control of the controller MC. The etching method according tovarious embodiments may be executed in the plasma processing apparatus 1by controlling the respective units of the plasma processing apparatus 1by the controller MC.

Hereinafter, a method MT will be described with reference to FIGS. 1 and3. FIG. 3 is a timing chart of an example related to the etching methodillustrated in FIG. 1. In FIG. 3, the vertical axis representsradio-frequency power, positive ion density, negative ion density,electron density, and output voltage of the power supply unit 64. InFIG. 3, the fact that the radio-frequency power is ON indicates that theradio-frequency power is supplied for plasma generation, and the factthat the radio-frequency power is OFF indicates that the supply of theradio-frequency power is stopped (afterglow state). In the middle partof the timing chart in FIG. 3, the solid line represents the positiveion density, the alternate long and short dash line represents theelectron density, and the dotted line represents the negative iondensity.

Further, reference is also made to FIGS. 4A to 6B. FIG. 4A is a diagramillustrating the state of plasma and a substrate in a period P1 in thetiming chart of FIG. 3, and FIG. 4B is a diagram illustrating the stateof plasma and a substrate in a period P2 in the timing chart of FIG. 3.FIG. 5A is a diagram illustrating the state of plasma and a substrate ina period P31 in the timing chart of FIG. 3, and FIG. 5B is a diagramillustrating the state of plasma and a substrate in a period P32 in thetiming chart of FIG. 3. FIG. 6A is a diagram illustrating the state ofplasma and a substrate in a period P4 in the timing chart of FIG. 3, andFIG. 6B is a diagram for explaining a step ST5 of the etching methodillustrated in FIG. 1. In the figures, a circle surrounding “+,” acircle surrounding “−,” a circle surrounding “e,” a circle surrounding“A,” and a circle surrounding “A*” represent a positive ion, a negativeion, an electron, an atom or a molecule, and a radical, respectively.Hereinafter, the method MT will be described by taking, as an example, acase where the plasma processing apparatus 1 is used in the execution.Further, in the following description, control of the respective unitsof the plasma processing apparatus 1 by the controller MC will also bedescribed.

The method MT is executed in a state where the substrate W placed on thesupport stage 16. The substrate W is held by the electrostatic chuck 20on the support stage 16. In an example, the substrate W includes a baseregion UR, a film EF, and a mask MK. The film EF is provided on the baseregion UR. The film EF is a film that is etched in the method MT. Themask MK is provided on the film EF. The mask MK provides an opening onthe film EF In the method MT, the pattern of the mask MK is transferredto the film EF. That is, an opening is formed in the film EF in themethod MT.

In the method MT, step ST1 is performed. In the step ST1,radio-frequency power is supplied to the lower electrode 18 (or theupper electrode 30) in order to generate plasma from the gas in thechamber 10. The gas may be continuously supplied into the chamber 10during the execution of the method MT. The radio-frequency power issupplied in the period P1 and the period P2, as illustrated in FIG. 3.The period P1 and the period P2 are execution periods of the step ST1.

The controller MC executes the first control in order to execute thestep ST1. In the first control, the controller MC controls the gassupply to supply gas into the chamber 10. In the first control, thecontroller MC controls the exhaust device 50 so as to set the pressurein the chamber 10 to a designated pressure. Further, in the firstcontrol, the controller MC controls the radio-frequency power source 61so as to supply radio-frequency power to the lower electrode 18 (or theupper electrode 30).

As illustrated in FIG. 4A, the plasma PL generated in the step ST1includes positive ions, negative ions, electrons, atoms or molecules,and radicals. In the plasma PL generated in the step ST1, the amount ofnegative ions is relatively small.

Step ST2 is executed during the execution of the step ST1. That is, thestep ST2 is executed during the supply of radio-frequency power forgenerating plasma. In the step ST2, as illustrated in FIG. 4B, anegative DC voltage is applied to the lower electrode 18 in order toetch the substrate W (i.e., the film EF) with positive ions from theplasma PL generated in the step ST1.

The controller MC executes the second control in order to execute thestep ST2. In the second control, the controller MC controls the powersupply unit 64 so as to apply a negative DC voltage to the lowerelectrode 18.

When the step ST2 is executed, positive ions collide with the substrateW and etch the substrate W. In the step ST2, since positive ions aresupplied to the substrate W, the substrate W is charged with a positivecharge as illustrated in FIG. 5A. In FIG. 5A, the symbol “+” in thesubstrate W indicates that the substrate W is charged with a positivecharge.

Subsequently, step ST3 is executed. In the step ST3, application of thenegative DC voltage to the lower electrode 18 is stopped in order togenerate negative ions. Further, in the step ST3, the supply ofradio-frequency power is stopped.

The controller MC executes the third control in order to execute thestep ST2. In the third control, the controller MC controls the powersupply unit 64 so as to apply a negative DC voltage to the lowerelectrode 18. Further, in the third control, the controller MC controlsthe radio-frequency power source 61 to stop supplying radio-frequencypower. Also, the gas supply may continuously supply gas to the chamber10 from the step ST1. The exhaust device 50 may continuously adjust thepressure in the chamber 10 from the step ST1.

In the step ST3 according to an embodiment, the application of thenegative DC voltage to the lower electrode may be stopped before thesupply of the radio-frequency power is stopped. In the third control ofthe embodiment, the controller MC may control the power supply unit 64so as to stop the application of the negative DC voltage to the lowerelectrode 18 before stopping the supply of the radio-frequency power tothe radio-frequency power source 61. According to the embodiment, anabnormal discharge is more reliably prevented.

In the period immediately after the start of the step ST3 (i.e., theperiod P31 in FIG. 3), the plasma PL includes positive ions, negativeions, electrons, atoms or molecules, and radicals as illustrated in FIG.5A. In the plasma PL, the number of negative ions is relatively small.

In an embodiment, step STm is performed during execution of the stepST3. In the step STm, the above-described parameter representing theelectron density in the chamber 10 is measured by the measuring device70. The parameter measured by the measuring device 70 is given to thecontroller MC.

In the subsequent step STa, it is determined from the parameter by thecontroller MC whether the electron density in the chamber 10 isdecreased so as to satisfy a predetermined standard. For example, whenthe electron density becomes smaller than a threshold value, it isdetermined that the electron density in the chamber 10 is decreased soas to satisfy a predetermined standard. Further, the decrease in theelectron density during the step ST3 reflects an increase in the amountof negative ions in the chamber 10.

When it is determined in the step STa that the electron density in thechamber 10 is not decreased so as to satisfy a predetermined standard,the step ST3 is continued. That is, the execution of the third controlby the controller MC continues. Meanwhile, when it is determined in thestep STa that the electron density in the chamber 10 is decreased so asto satisfy a predetermined standard, the step ST3 ends and the processproceeds to step ST4. That is, when it is determined from the parameterthat the electron density in the chamber 10 is decreased so as tosatisfy a predetermined standard, the controller MC ends the thirdcontrol and starts executing the fourth control.

During the execution of the step ST3, electrons are bonded to chemicalspecies such as atoms, molecules, or radicals in the chamber 10 togenerate negative ions. At the end of the step ST3 or a periodimmediately before the step ST3 (i.e., the period P32 in FIG. 3),sufficient negative ions are generated in the chamber 10 as illustratedin FIG. 5B.

In an embodiment, the step STm and the step STa may be omitted. In theembodiment, the step ST3 (and the third control) may be ended after apredetermined time has elapsed from the start time. The predeterminedtime is determined in advance as a time necessary for sufficientgeneration of negative ions in the chamber 10 after the start of thestep ST3.

The step ST4 is performed in the period P4 after execution of the stepST3. In the step ST4, in order to supply the negative ions generated inthe step ST3 to the substrate W, a positive DC voltage is applied to thelower electrode 18 in a state where the supply of radio-frequency poweris stopped.

The controller MC executes the fourth control in order to execute thestep ST4. In the fourth control of the embodiment, the controller MCcontrols the power supply unit 64 to apply a positive DC voltage to thelower electrode 18 in a state where the supply of radio-frequency powerto the radio-frequency power source 61 is stopped. Also, the gas supplymay continuously supply a gas to the chamber 10 from the step ST1. Theexhaust device 50 may continuously adjust the pressure in the chamber 10from the step ST1.

In the step ST4, since a positive DC voltage is applied to the lowerelectrode 18, negative ions are attracted to the substrate W, asillustrated in FIG. 6A. The negative ions collide with the substrate Wand etch the substrate W (i.e., the film EF). Negative ions also reducethe amount of positive charges on the substrate W.

As described above, in the method MT, a negative DC voltage is suppliedto the lower electrode 18 in a state where plasma is generated bysupplying radio-frequency power. As a result, positive ions collide withthe substrate W and etch the substrate W. Subsequently, the supply ofthe radio-frequency power and the application of the DC voltage to thelower electrode are stopped. Although the amount of negative ionsgenerated is small in a state where radio-frequency power is supplied,negative ions are efficiently generated by electrons which are attachedto chemical species in the gas when the supply of radio-frequency poweris stopped. Subsequently, a positive DC voltage is applied to the lowerelectrode 18 in a state where the supply of radio-frequency power isstopped. As a result, negative ions are supplied to the substrate W. Inthe method MT, negative ions reduce the amount of positive charges onthe substrate. Also, the substrate W is etched using both positive ionsand negative ions. Therefore, the etching efficiency is improved.

In an embodiment, an etching sequence ESQ including the step ST1, thestep ST2, the step ST3, and the step ST4 is executed one or more times.In the embodiment, the controller MC executes the etching controlsequence including the first control, the second control, the thirdcontrol, and the fourth control one or more times. When the etchingsequence ESQ is executed a plurality of times, the repetition frequencyof the etching sequence ESQ may be 10 kHz or more and 500 kHz or less.The repetition frequency of the etching sequence ESQ may be 50 kHz ormore and 400 kHz or less. Further, the frequency may be greater than 400kHz.

When the etching sequence ESQ is performed a plurality of times, themethod MT further includes step STb. In the step STb, it is determinedwhether the stop condition is satisfied. The stop condition is satisfiedwhen the etching sequence ESQ (or the etching control sequence) isperformed a predetermined number of times. When it is determined in thestep STb that the stop condition is not satisfied, the etching sequenceESQ (or the etching control sequence) is performed.

In an embodiment, when it is determined in the step STb that the stopcondition is satisfied, the step ST5 is performed. In the step ST5, thegas is exhausted from the internal space of the chamber 10 by theexhaust device 50. In the step ST5, the supply of radio-frequency powerby the radio-frequency power source 61 is stopped, and the applicationof the DC voltage to the lower electrode 18 by the power supply unit 64is stopped.

The controller MC performs the fifth control in order to execute thestep ST5. In the fifth control, the controller MC controls the exhaustdevice 50 so as to discharge a gas from the internal space of thechamber 10. In the fifth control, the controller MC controls theradio-frequency power source 61 so as to stop the supply of theradio-frequency power. Further, in the fifth control, the controller MCcontrols the power supply unit 64 so as to stop the application of theDC voltage to the lower electrode 18. In addition, the gas supply maycontinuously supply the gas to the chamber 10 from the step ST1, or maystop the supply of the gas during the execution period of the step ST5.

Etching byproducts generated by the etching sequence ESQ may be left inthe openings formed in the substrate W. When the step ST5 is executed,etching byproducts are discharged from the chamber 10 as gas, asillustrated in FIG. 6B. In FIG. 6B, a circle surrounding “B” representsan etching byproduct. In FIG. 5A, the symbol “+” in the substrate Windicates that the substrate W is charged with a positive charge.

In an embodiment, another sequence ASQ including one or more executionsof the etching sequence ESQ and the step ST5 may be repeated. Therepetition frequency of the sequence ASQ may be 100 Hz or more and 10kHz or less. A ratio of one or more execution periods of the etchingsequence ESQ in one execution period of the sequence ASQ may be 30% ormore and 70% or less. In the embodiment, the controller MC repeatedlyexecutes another control sequence. Another control sequence includes oneor more executions of the etching control sequence and a fifth control.In the embodiment, as illustrated in FIG. 1, the method MT includes stepSTc. In the step STc, it is determined whether the stop condition issatisfied. In the step STc, it is determined whether the stop conditionis satisfied. The stop condition is satisfied when the sequence ASQ (oranother control sequence) is executed a predetermined number of times.When it is determined in the step STc that the stop condition is notsatisfied, the sequence ASQ (or another control sequence) is executedagain. Meanwhile, when it is determined in the step STc that the stopcondition is satisfied, the method MT is ended.

In an embodiment, during one execution of the sequence ASQ, the step ST5may be executed for 10 μsec or more. In the embodiment, the fifthcontrol is executed for 10 μsec or more in the execution period of theother control sequence described above. In the embodiment, etchingbyproducts are more reliably discharged. As a result, the etchingefficiency of the substrate is further improved.

In an embodiment, the time length of the execution period of the stepST5 may be increased as the number of executions of the sequence ASQincreases. In the embodiment, the controller MC may increase the timelength of the execution period of the fifth control as the number ofexecutions of the other control sequence increases. In the embodiment,as the depth of the opening formed in the substrate W increases, thetime length of the execution period of the step ST5 is increased.Therefore, etching byproducts are more reliably discharged.

In an embodiment, radio-frequency power may be intermittently suppliedfrom the radio-frequency power source 61 to generate plasma during theexecution period of the step ST1, that is, in the period P1 and theperiod P2. That is, a plurality of pulses of radio-frequency power maybe intermittently supplied from the radio-frequency power supply 61during the execution period of the step ST1. In the embodiment, aplurality of pulses of radio-frequency power may be periodicallysupplied from the radio-frequency power supply source 61 during theexecution period of the step ST1. The cycle in which the pulses of theradio-frequency power are supplied from the radio-frequency power source61 may be a cycle defined by a frequency of 100 kHz or more and 1 MHz orless. In the embodiment, the power levels of the plurality of pulses ofthe radio-frequency power supplied from the radio-frequency power source61 during the execution period of the step ST1 may vary. In theembodiment, an average value of the power levels of the plurality ofpulses of the radio-frequency power supplied from the radio-frequencypower source 61 during the execution period of the step ST1 may vary inthe repetition of the etching sequence ESQ.

In an embodiment, a negative DC voltage may be intermittently appliedfrom the power supply unit 64 to the lower electrode 18 during theexecution period of the step ST2, that is, in the period P2. That is, aplurality of pulses of the negative DC voltage may be intermittentlyapplied from the power supply unit 64 to the lower electrode 18 duringthe execution period of the step ST2. In the embodiment, a plurality ofpulses of the negative DC voltage may be periodically applied from thepower supply unit 64 to the lower electrode 18 during the executionperiod of the step ST2. The cycle in which the pulses of the negative DCvoltage are applied from the power supply unit 64 to the lower electrode18 may be a cycle defined by a frequency of 100 kHz or more and 1 MHz orless. The timing at which the pulses of the negative DC voltage areapplied from the power supply unit 64 to the lower electrode 18 may besynchronized with the timing at which the pulses of the radio-frequencypower are supplied from the radio-frequency power source 61. In theembodiment, the voltage values of a plurality of pulses of the negativeDC voltage applied from the power supply unit 64 to the lower electrode18 during the execution period of the step ST2 may vary. In theembodiment, an average value of the voltage values of a plurality ofpulses of the negative DC voltage applied from the power supply unit 64to the lower electrode 18 in the execution period of the step ST2 mayvary in the repetition of the etching sequence ESQ.

In an embodiment, a positive DC voltage may be intermittently appliedfrom the power supply unit 64 to the lower electrode 18 during theexecution period of the step ST4, that is, in the period P4. That is, aplurality of pulses of the positive DC voltage may be intermittentlyapplied from the power supply unit 64 to the lower electrode 18 duringthe execution period of the step ST4. In the embodiment, a plurality ofpulses of the positive DC voltage may be periodically applied from thepower supply unit 64 to the lower electrode 18 during the executionperiod of the step ST4. The cycle in which the pulses of the positive DCvoltage are applied from the power supply unit 64 to the lower electrode18 may be a cycle defined by a frequency of 100 kHz or more and 1 MHz orless. In the embodiment, the voltage values of a plurality of pulses ofthe positive DC voltage applied from the power supply unit 64 to thelower electrode 18 during the execution period of the step ST4 may vary.In the embodiment, an average value of the voltage values of a pluralityof pulses of the positive DC voltage applied from the power supply unit64 to the lower electrode 18 during the execution period of the step ST4may vary in the repetition of the etching sequence ESQ.

Although various embodiments have been described above, the presentdisclosure is not limited to the embodiments described above, andvarious omissions, substitutions, and changes may be made. In addition,it is possible to combine the elements in other embodiments to formother embodiments.

For example, the plasma processing apparatus 1 is a capacitively coupledplasma processing apparatus, but the plasma processing apparatusaccording to another embodiment may be another type of plasma processingapparatus such as an inductively coupled plasma processing apparatus.Further, the method MT may be performed using any type of plasmaprocessing apparatus other than the plasma processing apparatus 1, forexample, an inductively coupled plasma processing apparatus.

According to an embodiment, the amount of positive charges on thesubstrate may be reduced and the etching efficiency may be increased.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. An etching method performed in a plasmaprocessing apparatus, the etching method comprising: placing a substrateon a substrate support provided in a chamber of the plasma processingapparatus; supplying a radio-frequency power to generate plasma from agas in the chamber; applying a negative DC voltage to a lower electrodeof the substrate support during the supplying of the radio-frequencypower, thereby etching the substrate with positive ions from the plasma;stopping the applying of the negative DC voltage to the lower electrodeand the supplying of the radio-frequency power, thereby generatingnegative ions; and applying a positive DC voltage to the lower electrodein a state where the supplying of the radio-frequency power is stopped,thereby supplying the negative ions to the substrate.
 2. The methodaccording to claim 1, further comprising: discharging a gas from aninternal space of the chamber in a state where the supplying of theradio-frequency power is stopped and the applying of the DC voltage tothe lower electrode is stopped after one or more executions of anetching sequence including the supplying of the radio-frequency power,the applying of the negative DC voltage, the stopping, and the applyingof the positive DC voltage.
 3. The method according to claim 2, whereinanother sequence including the one or more executions of the etchingsequence and the discharging is repeated.
 4. The method according toclaim 3, wherein the discharging is executed for 10 sec or more in anexecution period of the another sequence.
 5. The method according toclaim 3, wherein a time length of the execution period of thedischarging is increased as a number of executions of the anothersequence increases.
 6. The method according to claim 1, wherein aparameter representing an electron density in the chamber is measuredduring execution of the stopping, and when determined from the parameterthat the electron density in the chamber is decreased to satisfy apredetermined standard, the applying of the negative DC voltage isstarted.
 7. The method according to claim 1, wherein in the stopping,the applying of the negative DC voltage to the lower electrode isstopped before the supplying of the radio-frequency power is stopped. 8.The method according to claim 1, wherein in the supplying of theradio-frequency power, a plurality of pulses of the radio-frequencypower are intermittently supplied to generate the plasma.
 9. The methodaccording to claim 1, wherein in the applying of the negative DCvoltage, a plurality of pulses of the negative DC voltage areintermittently applied to the lower electrode.
 10. The method accordingto claim 1, wherein in the applying of the positive DC voltage, aplurality of pulses of the positive DC voltage are intermittentlyapplied to the lower electrode.
 11. A plasma processing apparatuscomprising: a chamber; a substrate support having a lower electrode andprovided in the chamber; a radio-frequency power source configured tosupply radio-frequency power to generate plasma from a gas in thechamber; a power supply electrically connected to the lower electrodeand configured to generate a positive DC voltage and a negative DCvoltage; and a controller configured to control the radio-frequencypower source and the power supply, wherein the controller is configuredto execute: a first control that controls the radio-frequency powersource to supply the radio-frequency power to generate plasma from thegas in the chamber; a second control that controls the power supply toapply the negative DC voltage to a lower electrode of the substratesupport during the supplying of the radio-frequency power, therebyetching a substrate with positive ions from the plasma; a third controlthat controls the power supply and the radio-frequency power source tostop the applying of the DC current voltage to the lower electrode andthe supplying of the radio-frequency power, thereby generating negativeions; and a fourth control that controls the power supply to apply thepositive DC voltage to the lower electrode in a state where thesupplying of the radio-frequency power is stopped, thereby supplying thenegative ions to the substrate.
 12. The apparatus according to claim 11,further comprising: an exhaust device connected to the chamber, whereinthe controller is configured to further execute a fifth control thatcontrols the exhaust device to exhaust a gas from an internal space ofthe chamber in a state where the supplying of the radio-frequency poweris stopped and the applying of a DC voltage to the lower electrode isstopped after one or more executions of an etching control sequenceincluding the first control, the second control, the third control, andthe fourth control.
 13. The apparatus according to claim 12, wherein thecontroller repeatedly executes another control sequence including one ormore executions of the etching control sequence and the fifth control.14. The apparatus according to claim 13, wherein the fifth control isexecuted for sec or more in an execution period of the another controlsequence.
 15. The apparatus according to claim 13, wherein thecontroller increases a time length of an execution period of the fifthcontrol as a number of executions of the another control sequenceincreases.
 16. The apparatus according to claim 11, further comprising:a measuring device that measures a parameter representing an electrondensity in the chamber during execution of the third control, whereinthe controller starts execution of the fourth control when determinedfrom the parameter that the electron density in the chamber is decreasedto satisfy a predetermined standard.
 17. The apparatus according toclaim 11, wherein in the third control, the controller controls thepower supply to stop the applying of the negative DC voltage to thelower electrode before stopping the supplying of the radio-frequencypower.
 18. The apparatus according to claim 11, wherein in the firstcontrol, the controller controls the radio-frequency power source tointermittently supply a plurality of pulses of the radio-frequencypower, thereby generating the plasma.
 19. The apparatus according toclaim 11, wherein in the second control, the controller controls thepower supply to intermittently apply a plurality of pulses of thenegative DC voltage to the lower electrode.
 20. The apparatus accordingto claim 11, wherein in the fourth control, the controller controls thepower supply to intermittently apply a plurality of pulses of thepositive DC voltage to the lower electrode.